The long-term objectives of this project are to elucidate the mechanisms responsible for deficient HLA Class I antigen expression in certain malignant tumor cells and to increase the understanding of the mechanisms by which interferons regulate Class I gene expression in these malignant cells. It is anticipated that by increasing the understanding of the basic control mechanisms involved, more successful use of the interferons in the therapy of currently incurable malignancies will be possible. Several specific questions will be addressed to achieve these objectives. 1) What factors cause deficient HLA Class I expression in malignant cells which contain apparently structurally intact genes? This question will be approached by use of molecular genetic analysis of HLA Class I gene expression in the K562 human leukemia cell line. This analysis is made possible by recombinant DNA clones containing HLA-Class I genes, and by transient and long-term DNA-mediated gene transfer assays. 2) Are specific nuclear factors involved in suppression of HLA Class I gene expression and if so how do these factors function? This question will be addressed by employing biochemical techniques to isolated nuclear factors which bind to regulatory sequences of Class I genes as well as by surrogate genetic approaches using recombinant DNA technology. 3) Is post-transcription regulation a major factor in interferon mediated modulation of Class I gene expression in K562 leukemia cells and what is the molecular basis for this regulation? A combination of DNA mediated gene transfer experiments and biochemical approaches will be applied to this question. 4) What are the immunologic effects of up- regulation of HLA Class I expression in K562 tumor cells. Cytotoxic T-cell killing assays, lymphokine activated killer cell lysis assays and natural killer cell assays will be performed on cells which have been treated to maximize Class I expression. Besides the specific information related to regulation of Class I gene expression in tumor cells by the action of interferons which could have relatively direct clinical implications, it is anticipated that the knowledge gained about basic mechanisms controlling Class I gene expression should have broader application in understanding the normal function of the crucial component of the human immune system.